Hawke’s Bay public health officials today welcome the release of an Institute of Environmental Science and Research (ESR) report into any potential long-term health impacts from silt following Cyclone Gabrielle saying the findings are “extremely reassuring”.

Health New Zealand | Te Whatu Ora National Public Health Service commissioned the report following Cyclone Gabrielle to better understand any longer-term impacts of silt or dust on human health.

Medical Officer of Health Dr Bridget Wilson said findings set out in the report followed a robust study by ESR drawing on analysis from flooding events overseas, as well as in-depth local analysis on silt sampling and air quality.

“Impacted communities have been understandably concerned about the effect of silt and dust on their health and what that could mean longer term,” said Dr Wilson.

“This report was commissioned to ensure an in-depth analysis by scientists in order to provide the best possible information to support the health and wellbeing of our communities, including identifying any additional measures that may be required to further protect public health.

“It is therefore extremely reassuring to share that ESR’s investigations have determined the likelihood of long-term public health impacts following silt and dust exposure is deemed low.”

ESR Science Leader, Risk Assessment, Food and Social Systems Group Peter Cressey, said the investigations included a review of international evidence related to the health effects of flooding events, as well as extensive silt contamination analysis and air quality monitoring post Cyclone Gabrielle.

“The report concluded that while health effects may occur due to flooding events, this is most commonly due to direct contact with flood waters, rather than flood-deposited silt.”

“Communities concerned about crystalline silica in silt and the risk of silicosis can be reassured that silt contains no more crystalline silica than normal garden soil and less than most beach sand.

“Air quality monitoring in the Hawke’s Bay region during September 2023 to March 2024 also indicated a low level of concern for silicosis resulting from exposure to silt in the form of airborne dust.”

Mr Cressey concluded that the long-term health risks from contact with cyclone-deposited silt are no greater than those from our day-to-day environment.

“Those affected by Cyclone Gabrielle have a range of huge issues to deal with. All the evidence indicates that long-term health effects due to silt will not be one of those issues.”

Health NZ says while the results of the study on long-term health impacts are very reassuring, public health advice remained in place to support people who experienced short- term symptoms like eye and airway irritations from dust.

“People continue to be advised to wear a mask when outside on dusty days or when undertaking clean up around their property that generates dust,” Dr Wilson said, adding the Silt Recovery Taskforce also continued its work to minimise dust impacts.

The Silt Recovery Taskforce, a collaboration between Hawke’s Bay Regional Council and Hastings District Council, aims to reduce dust as much as possible with standard practice of water spraying, and provides guidance to landowners to reduce the risk of airborne silt. This includes crop cover and the grassing of open paddocks as soon as possible on completion of remedial works.

The full report is available here.

 

ENDS

 

Media Contacts:

Health New Zealand: hnzmedia@tewhatuora.govt.nz

ESR: media@esr.cri.nz

 

Supporting community recovery from Cyclone Gabrielle: Contamination resulting from flooding events

Frequently Asked Questions:

 

Why was the report commissioned?

Health New Zealand | Te Whatu Ora National Public Health Service commissioned the report to make sure that there was a full understanding of any long-term health impacts related to silt and dust following the significant flooding and environmental impacts of Cyclone Gabrielle.

 

What were the key findings of the study?

  • Adverse health effects may occur due to flooding However, health effects are most commonly associated with direct contact with flood water, rather than flood- deposited silt.
  • Increases of chemical contaminant concentrations in silt/soil due to flooding events can generally be linked to known or suspected contamination scenarios, such as deposition of river sediments where those sediments were known to be highly
  • Concentrations of faecal indicator bacteria and pathogens decrease in surface silts/soils over time following the flooding event, as they are exposed to sun and
  • Analysis of chemical contaminants in flood-deposited silt from Cyclone Gabrielle either did not detect the contaminants or found that their mean concentrations were consistent with background levels and within soil guideline levels.
  • Air quality monitoring in the Hawke’s Bay region during September 2023 to March 2024 indicated a low level of concern for silicosis resulting from exposure to silt in the form of airborne dust.
  • Asbestos was not detected in any of the silt samples

 

What did the study find about the risk of getting sick from contact with the flood water and silt?

Reports from overseas study show increased risks of gastroenteritis (stomach upset), skin problems (rashes or dermatitis) and respiratory tract problems (cough, throat irritation, sinus congestion) following contact with flood water. Health issues have also been reported due to transmission of gastrointestinal or respiratory illness in crowded evacuation centres. There is little evidence of people getting sick from contact with silt.

 

What did the study find about the level of contamination in the silt?

Almost 1000 silt samples were taken following Cyclone Gabrielle and tested for chemical and microbiological contaminants. Levels of ‘heavy metals’ – lead, cadmium, arsenic and the like – were generally the same as background soil levels for the same areas and were well within guideline levels. Petrol residues and pesticides were occasionally detected but only at very low levels – well below levels that would be a health concern. Levels of bacteria were higher than usual in some silt samples immediately after the cyclone, particularly in the area around the Napier wastewater treatment plant. However, bacteria levels dropped quite quickly as the silt dried out.

 

I live in Awatoto, there were concerns about chemical contaminants. Was silt tested and what were the results?

Samples were taken from the Awatoto area soon after the cyclone. Findings were pretty much what you would expect – some petrol and other chemical residues at industrial sites, and higher bacteria levels around the wastewater treatment plant. Otherwise, the silt was similar to soil from the same area and no causes for long-term concern were found.

 

What is the risk to communities of developing silicosis following exposure to dust?

Silicosis is caused by long-term exposure to high levels of ‘crystalline silica’. Soil, silt and sand naturally contain some crystalline silica, mainly in the form of quartz. Analysis of the quartz content of the silt and monitoring of dust levels in the air through spring and summer confirmed that the exposure of the communities to crystalline silica was well below levels that might cause silicosis. It should be stressed that the monitoring represents the ‘worst case’: the guidelines for crystalline silica are for a lifetime of exposure; furthermore exposure will be lower through autumn and winter and will further decrease as plant regrowth reduces the amount of dust in the air.

 

I live in an affected community which hasn’t had air quality monitoring, are the findings of this study still relevant to me?

The air quality monitoring sites were specifically selected to cover areas where the airborne dust levels were worst. The risks from airborne dust and crystalline silica at other sites are likely to be a lot lower.

 

Dust in the Esk Valley is concerning a lot of us. What did the study find?

The guideline safe level of exposure to crystalline silica over a lifetime is 3 μg/m3. Dust levels were worst in the Esk Valley in October 2023. The average estimated air level of crystalline silica during this period was 0.6 μg/m3. In fact exposure would have been lower, as people are not outside all of the time and dust levels are lower inside.

 

Should communities still be trying to reduce their exposure to dust?

Although the information gathered confirms that the risk of silicosis is negligible, airborne dust can still be an irritant and an extra burden for people with existing breathing problems, such as asthma sufferers.

 

I still have health concerns. Who should I talk to?

While the results of the report are very reassuring that the risk of long-term health impacts are low, for those with any concerns about their health should phone Healthline on 0800 611 116 or see their GP.